Variable baffle for translating devices



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1M 2 o M l m I T l J HIM 1 am A y a F H J m fl d F e VARIAB-LJE BAFFLEFOR TRANSLATING DEVICES Fails. 22, 1944.

Patented Feb. 22, 1944 "UNITED T OFFICE 2,342,334 'vlfitrdnm 'B'AFTifLEFOR TRANSLATING DEVICES Fl ank J. Faltico,-Minneapolis, Minn, assigno'rto The Maico Company Incorporated, Minneapolis, Minn., acorporation ofMinnesota Application July 11, 1942, Serial No. 450,600

8'Claims. This invention relates generally to improvements intranslating devices, such as headphones, and more 'particularly to meansfor adiusting the baffle efiectin such devices'to thereby securevariations in frequency response.

The primary object of the'invention is to proivide means whereby'thebaffle effect of theusual headphone may be easily an quickly varied bypermitting the passage of airwaves between the front or outer side ofthe diaphragm and the back or inner side thereof. ZBy this means theusualinfinite baffle of such devices may be altered according torequirements and the frequency response varied by permitting at leastthe partial 1 cancellation of unwanted frequencies in the audio range.Another object is to provide means of this nature in any extremelysimple and practical'formembodying simply an air passage-waycommunicating with the opposite sides of the diaphragm and a memberarranged to adjustably open or close said passage-way and therebycontrol the volume of air passing therethrough.

These and other more detailed and specific objects will be disclosed inthe course of the following specification, referenc being had to theaccompanying drawing, in which- Fig. 1 is a diametricalsection throughaheadphone type of translating device showing my invention embodiedtherein. A

Fig. 2 is an inside elevation or plan view of the cap forming part ofthe structure of Fig. 1, showing the adjusting screw removed.

Fig. 3 is an enlarged, fragmentary cross sectional view illustrating thecommunication between opposite sides'of the diaphragm.

Fig. 4 is a face or plan view-of the body or case'member forming part ofthe headphone, a portion thereof being shown in section.

Referring now more'particula'rly and by reference characters to thedrawing, a headphone type of translator or receiv'er'is shown embodyingessentially a casing or body member A having an annular shell B againstthe'end of which the vibrating diaphragm 'Cis placed and held by 'acap'D, said cap being's c'rewed onto the body member as indicated at E(or otherwise fastened) and 'having'a central opening F for thep'a'ssageof sound waves formed byvibrati'on of the diaphragm. Anelectromagnetic "vibrating or driving motor or device G is secured tothe body member 'A as clearly shown and includes wire wound pole piecesH disposed adjacent the diaphragm C.

The foregoing constitutes the usual construction of such units and noinvention is herein claimed for such construction 'per se. In operation,the diaphragm 'C isvibrated'by the mechanism G in accordance 'With thevariations in electrical current flowing therein, and such vibrationscause the formation of sound waves in the air which are emitted from thediaphragm and are audible to the ear. Obviously only 'the sound Wavesformed by the outer, or 'as usually termed, front side C of thediaphragm will be audible and the waves formed by the inner, orproperly, rear side or back '0" of the diaphragm will be confined to thecavity formed between body member A and cap D. Accordingly there will beno cancellation of certain frequencies by the movement of out of phasesound waves from front to back of the diaphragm, as occurs where thereis means of communication between opposite-sides, and the frequencyresponse is there- 'fore substantially fiat or level throughout itsrange. The effect isas though there were a baffle of infinite size suchthat no frequencies could possibly reach the back of the diaphragm in:proper phase relation to cause cancellation.

Such fiat frequency response is a disadvantage under some circumstancessuch as Where the unit is used primarily for voice and communicationwork, or particularly where the unit is a part of a hearing aid devicefor use by the hard of hearing. 'In such cases it is very desirable tovary the frequency response to effectively accentuate desiredfrequencies by the reduction or cancellation of unwanted or uselessfrequencies. For example, most persons having diificulty in hearing havebetter perception at certai'n frequencies than at others, andthe'adjustment of the response of the unit to-givemaXimum effect to thefrequencies at which hearingloss is greater is obviously desirable. Inaccordance with my invention, therefore, I provide means for varying theba'fiie eiTect of the casing'andcap upon the diaphragm C as will'now bedescribed.

The cap D is formed with a'shoulder or ledge I0 adapted to bear againstthe margin of the diaphragm and press it against the end of the shell B,and'to thus provide space I I for vibratory movement of the diaphragm. Iprovide, then, a channel or groove l2 in this ledge at one point (ormore) extending radially therein -and communicating with the space H atthe front of "the diaphragm. This channel also communicates with asimilar (or continuation) channel or groove [3 formed in the interiorannular surface M of the cap D which contacts the corresponding annularouter surface id of the shell 33. In this shell there is formed aradially extending opening It which registers at its outer end with thechannel [3 and at its inner end communicates with the cavity back or atthe rear of the diaphragm. At a point radially aligned with the openingit the cap D has in its flange or outer wall IT a tapped opening orsocket l8 opening into the channel It and in which is placed a threadedplug or screw E9. The screw may obviously be moved inward or outward inthe opening l8 by a screw driver inserted through the open outer endthereof. The screw or plug I9 is preferably larger in di-' ameter thanthe opening It or the width of channel 13 so that they may be completelyclosed oif when the plug is screwed inward as seen in Fig. 1.

Essentially, then, the invention is seen to comprise an air passage,channel or vent, made up by the channels |2I3 and the opening it,communicating at its ends with the opposite front and rear sides of thediaphragm C, and with means, formed here by the plug or screw Iii, toopen or close this passage and vary the effective capacity thereof. Itis evident that when the plug I9 is screwed inward as far as possiblethe communication between front and rear of the diaphragm is entirelyout off and the baffle effect is infinite. As the plug is drawnoutwardly the passage-way is gradually opened permitting the flow of airfrom front to back of the diaphragm in greater or lesser volume ordegree as indicated in Fig. 3, to thus gradually reduce the baffleefiect and accordingly vary the effective frequency response of theunit. Such adjustment may be readily carried out to any degree requiredand, since the plug H) is carried wholly by the cap D, the removal ofthis cap for any reason will not affect the adjustment, once it is made.

It is understood that suitable modifications may be made in thestructure as disclosed, provided such modifications come within thespirit and scope of the appended claims. Having now therefore fullyillustrated and described my invention, what I claim to be new anddesire to protect by Letters Patent is:

1. In a device of the character described, a

vibratory diaphragm, a casing supporting the said diaphragm and having aportion enclosing one side of the diaphragm and isolating that side fromthe opposite side and thereby causing an infinite baffle effect, saidcasing having a passage-way connecting the opposite sides of thediaphragm, and means associated with the casing for opening and closingthe said passageway to control the flow of air from one side of thediaphragm to the other.

2. In a headphone of the character described, a casing, a diaphragmmarginally supported in the casing and having its front side exposed buthaving its rear side enclosed by said casing, an air passage meansformed in the casing and communicating at its respective ends with thefront and rear sides of the diaphragm, and means for varying theefiective size of the said air passage means to thereby vary the bafileeffect of'the casing upon sound waves emitted by the diaphragm.

3. In a headphone of the character described, a casing comprisinga bodymember and a cap member removably mounted thereon, a dia phragmsupported by the casing in such manner as to be exposed at its frontside and enclosed at its rear side, and air passage means for permittingthe limited passage of air between front and rear sides of thediaphragm, the said air passage means being formed in part in the bodymember and in part in the cap member.

4. In a headphone of the character described, a casing comprising a bodymember and a cap member removably mounted thereon, a diaphragm supportedby the casing in such manner as to be exposed at its front side andenclosed by the casing at its rear side, and air passage means forpermitting the limited passage of air between front and rear sides ofthe diaphragm, the said air passage means being formed in part in thebody member and in part in the cap member, and means carried by the capmember and operative to enter the air passage means to vary theefiective size thereof.

5. In a headphone of the character described, a casing comprising a bodymember and a cap member removably mounted thereon, a diaphragm supportedby the casing and enclosed at its rear side by said casing, the said capmember having an opening to partially expose the front side of thediaphragm, and the said body member and cap member having respectivelyan opening and a channel forming a means for conducting air betweenfront and rear sides of the diaphragm.

6. In a headphone of the character described, a casing comprising a bodymember and a cap member removably mounted thereon, a diaphragm supportedby the casing and enclosed at its rear side by said casing, the said capmemher having an opening to partially expose the front side of thediaphragm, the said body member having an opening communicating with therear side of the diaphragm, and the said cap member having a channelcommunicating with the front side of the diaphragm and adapted also tocommunicate with the said opening when the cap member is mounted uponthe body member.

7. In a headphone of the character described, a casing comprising a bodymember and a cap member removably mounted. thereon, a diaphragmsupported by the casing and enclosed at its rear side by said casing,the said cap member having an opening to partially expose the front sideof the diaphragm, the said body member having an opening communicatingwith the rear side of the diaphragm, the said cap member having achannel communicating at its respective ends with the said opening andwith the front side of the diaphragm, and a plug threaded in the capmember and operative to adjustably open and close the said channel.

8. In a headphone of the character described, a casing including a bodymember having a re.- cess in one side, a diaphragm mounted at one sidevover the recess and adapted when vibrated to transmit sound wavevibrations from both its sides, a cap member mounted over the other sideof the diaphragm, and means in the body member and cap member providingcommunication for the passage of sound waves between the opposite sidesof the diaphragm.

FRANK J. FALTICO.

